The invention relates generally to a friction clutch pack having a ball ramp operator and more specifically to a friction clutch pack having a ball ramp operator actuated by a bi-directional electric motor.
Notwithstanding significant sales of light and medium duty trucks, an emphasis upon improved vehicle performance and gas mileage remains. Within the arena of engineering details, this emphasis takes several forms. The first is the obvious approach of weight reduction. Such weight reduction exempts virtually no part of the vehicle: engine, power train, chassis, suspension, steering gear body, seating, windows, and options.
The high gas mileage goal also affects the design of electrical components as reducing current consumption has a corresponding affect on gas consumption. This emphasis has encouraged the use of electrical devices which exhibit reduced current consumption. Components which exhibit both significant power consumption and have a significant duty cycle, such as electric clutches, are carefully studied.
One such class of clutches is referred to as ball ramp clutches. These clutches, in addition to a friction plate or multiple plate friction clutch pack, include an operator comprising a pair of adjacent circular plates having a plurality of opposed arcuate ramped recesses which each receive a ball bearing. Relative rotation of the circular plates causes the ball bearings to ride up the ramps of the recesses and separate the plates, thereby engaging the clutch. An electromagnetic coil may be utilized to create drag which causes the plates to rotate relatively. In this design, it is the speed differential and the energy of such speed differential which causes engagement of the clutch. That is, the electromagnetic force generated by the electromagnetic coil does not directly engage the clutch but acts upon the ball ramp operator which, in turn, engages the clutch. So configured the electromagnetic coil can be significantly smaller and consume less electricity than a direct acting clutch. In addition to the weight reduction, heat dissipation is also a less significant concern. Thus, overall, a ball ramp clutch can be significantly more compact than a direct acting electromagnetic clutch.
Actuation of the clutch, however, does require relative rotation, that is, a speed difference between the input and the output of the clutch. This is seldom an operational disadvantage, however, inasmuch as if there is no speed difference, there is no need to engage the clutch and, in fact, engagement requires only the smallest speed differential.
Nonetheless, the ability to effect clutch engagement independent of a shaft speed differential is seen as a benefit in certain operational conditions. The present invention addresses this desire.